The project continues to center on efforts to understand the mechanisms which control the hepatic restorative process - post-resection regeneration. Studies attempt to isolate this cell division phenomenon in an in vitro system, employing both (a) liver cell cultures and (b) serum and serum factors drawn from animals during regneration. Studies of the unusual in vitro growth characteristics of cells from regenerating liver are continued employing soft agar culture techniques. Cells from regenerating liver (rat and mouse) form colonies in soft agar and modifications in technique will be made to stimulate hepatocyte colony formation and note the effect of post hepatectomy serum in the system. A technique has been adapted for monitoring the regenerative response (dog) employing in vitro H3-thymidine uptake of fresh liver biopsy cores. The sensitivity of this technique will be determined employing graded hepatic resections, serial liver ablations; and the effects of post hepatectomy serum on the uptake determined. Continued studies of the "inhibition" of in vitro growth in cells removed during the immediate post hepatectomy period (rat) will employ suspension cultures. The isolation perfusion with a labeling compound in media of livers during different phases in the regenerative response will be pursued employing hormonal additives to the perfusate to determine H3-thymidine uptake effects of these additives.